Thermoelectric devices are used to convert temperature differences to electric voltage. These thermoelectric devices can be used in sensors, for recycling waste heat, for increasing auto fuel efficiency, for solar energy conversion, or in other devices. For example, current solar cells do not convert low frequency heat energy. A combined solar and thermoelectric system will convert more solar radiation into electricity and increase efficiency of the solar cell. Of course, other devices also can benefit from thermoelectric energy conversion.
FIG. 1 is a view of an embodiment of a thermoelectric device. If a temperature gradient is formed in a thermoelectric material, an electric potential or voltage will be produced by this temperature difference due to the Seebeck effect. If the hot ends of the n-type and p-type materials are electrically connected and a load is connected across the cold ends of the n-type and p-type materials, then the voltage produced by the Seebeck effect will cause current to flow through the load. This will generate electrical power.
Thermoelectric conversion efficiency is determined by a material property known as the thermoelectric Figure of Merit (zT). zT is defined as:zT=(αS2T)/κwherein α is electrical conductivity, κ is thermal conductivity, S is the Seebeck coefficient, and T is temperature. Increasing α while decreasing κ is needed to improve zT. Currently, the best zT for a material is approximately 1.6. FIGS. 2-3 illustrate zT for several known p-type and n-type thermoelectric materials. The low zT value of current materials limits new thermoelectric applications that may require a higher zT value. What is needed is an improved thermoelectric material or, more particularly, a porous film for thermoelectric applications.